Ecoregions denote areas of general similarity in ecosystems and in type, quality, and quantity of environmental resources. They are designed to be a spatial framework for research, assessment, management, and monitoring of ecosystems and ecosystem components. Ecoregions stratify the environment by its probable response to disturbance (Bryce and others, 1999). These general-purpose regions are critical to the structuring and implementation of ecosystem management strategies across Federal agencies, State agencies, and non-governmental organizations responsible for different types of resources within the same geographical areas (Omernik and others, 2000).
Ecological and biological diversity of Texas is enormous. The state encompasses barrier islands and coastal lowlands, large river floodplain forests, rolling plains and plateaus, forested hills, deserts, and a variety of aquatic habitats. There are 12 level III ecoregions and 56 level IV ecoregions in
Texas, and most continue into ecologically similar parts of adjacent states in the U.S. or Mexico.
This map is based on the premise that ecological regions are hierarchical and can be identified through analysis of spatial patterns and the composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity (Wiken, 1986; Omernik 1987, 1995). These phenomena include geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. The relative importance of each characteristic varies from one ecological region to another.
A hierarchical scheme indicates different levels of ecological regions. Level I divides North America into 15 ecological regions. Level II divides the continent into 52 regions (Commission for Environmental Cooperation Working Group, 1997). At level III, the continental United States contains 104 ecoregions,
and the conterminous United States has 84 ecoregions (U.S. Environmental Protection Agency, 2003). Level IV, depicted here for Texas, is a further refinement of level III ecoregions. Explanations of the methods used to define the U.S. Environmental Protection Agency's (EPA) ecoregions are given in Omernik (1995), Omernik and others (2000), and Gallant and others (1989).
This map is modified from a collaborative project between EPA Region VI, EPA National Health and Environmental Effects Research Laboratory (Corvallis, Oregon), the Texas Commission on Environmental Quality (TCEQ), and the U.S. Department of Agriculture- Natural Resources Conservation Service (NRCS). Collaboration and consultation also occurred with the U.S. Geological Survey (USGS)-Earth Resources Observation Systems Data Center.
Bryce, S. A., Omernik, J. M., and Larsen, D. P., 1999, Ecoregions- a geographic framework to guide risk characterization and ecosystem management: Environmental Practice, v. 1, no. 3, p. 141-155.
Commission for Environmental Cooperation Working Group, 1997, Ecological regions of North America- toward a common perspective: Montreal, Quebec, Commission for Environmental Cooperation, 71 p.
Gallant, A. L., Whittier, T. R., Larsen, D. P., Omernik, J. M., and Hughes, R. M., 1989, Regionalization as a tool for managing environmental resources: Corvallis, Oregon, U.S. Environmental Protection Agency, EPA/600/3-89/060, 152 p.
Omernik, J. M., 1987, Ecoregions of the conterminous United States (map supplement): Annals of the Association of American Geographers, v. 77, no. 1, p. 118-125, scale 1:7,500,000.
______ 1995, Ecoregions- a spatial framework
for environmental management, in Davis, W. S., and Simon, T. P., eds., Biological assessment and criteria- tools for water resource planning and decision making: Boca Raton, Florida, Lewis Publishers, p. 49-62.
Omernik, J. M., Chapman, S. S., Lillie, R. A., and Dumke, R. T., 2000, Ecoregions of Wisconsin: Transactions of the Wisconsin Academy of Sciences, Arts and Letters, v. 88, no. 2000, p. 77-103.
U.S. Environmental Protection Agency, 2003, Level 111 ecoregions of the continental United States (revision of Omernik, 1987): Corvallis, Oregon, U.S. Environmental Protection Agency- National Health and Environmental Effects Research Laboratory, Map M-l, various scales.
Wiken, E., 1986, Terrestrial ecozones of Canada: Ottawa, Environment Canada, Ecological Land Classification Series No. 19, 26 p.
The BEG acknowledges James M. Omernik, Principal Investigator, EPA, and Anne Rogers, Texas Commission on Environmental Quality (TCEQ), for assistance and permission to reproduce this map.
managing editor: Peter Eichhubl media manager: Cathy J. Brown graphics: John T. Ames and Jamie H. Coggin
authors: Glenn E. Griffith (Dynamac Corporation), Sandra A. Bryce (Dynamac Corporation), James M. Omernik (USGS), Jeffrey A. Comstock (Indus Corporation), Anne C. Rogers (TCEQ), Bill Harrison (TCEQ), Stephen L. Hatch (Texas A&M University), and David Bezanson (Natural Area Preservation Association).
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